Definition of Universal Naming Convention (UNC) in The Network Encyclopedia.
What is the Universal Naming Convention (UNC)?
UNC stands for Universal Naming Convention, is a convention for naming shared network resources.

The syntax for a Universal Naming Convention (UNC) path to a network resource is as follows:
\\server_name\share_name[\path]
The server_name Section
The server_name portion of a Universal Naming Convention name can consist of either a network name string (the name of a shared folder) set by an administrator and maintained by a network naming service like DNS or WINS or by an IP address.
These hostnames normally refer to either a Windows PC or a Windows-compatible printer.
The share_name Section
The share_name portion of a Universal Naming Convention pathname references a label created by an administrator or, in some cases, within the operating system.
The built-in share name admin$ refers to the root directory of the operating system installation – usually C:\Windows but sometimes C:\\WINDOWS or C:\\WINNT.
UNC paths do not include Windows driver letters, only a label that may reference a particular drive.
The File_Path Section
The optional file_path portion of a Universal Naming Convention name references a local subdirectory beneath the share section. This part of the path is optional.
When no file_path is specified, the UNC path simply points to the top-level folder of the share.
The file_path must be absolute. Relative paths are not allowed.
UNC example
The UNC path \\max\sales\1998\report.doc indicates that the document report.doc is located within the shared folder called sales on the file server called max. The document is in the 1998 subfolder of the sales shared folder.